The present invention relates to inclinometers or tilt sensors and, more specifically, an accelerometer based tilt sensor and method for using the same.
Accelerometers are often mounted to various devices and are used to measure the degree of tilt of the device with respect to a horizontal axis. Accelerometers act under the acceleration of gravity and sense deviations in the gravitational field. Specifically, as an accelerometer is tilted at an angle with respect to the horizontal, the vertical component of the force of gravity acting on the accelerometer changes, causing the electronic components within the accelerometer to react differently, and varying the output reading of the accelerometer. Some accelerometers utilize a piezoelectric crystal and a mass whereby the changing angle of inclination causes the mass to apply varying pressure on the piezoelectric crystal, which produces the output signal. In other accelerometers, a capacitor and resistor are used to effectively create a mass-spring system whereby the output signal varies under the force of gravity with the tilt angle.
Conventional accelerometer based tilt sensors use a separate accelerometer for each axis of rotation. For example, a typical two-axis tilt sensor utilizes two accelerometers. For purposes of error correction, an additional accelerometer typically is used for each axis of rotation. In other words, to achieve redundancy with a two-axis tilt sensor, four accelerometers are necessary.
One disadvantage with conventional accelerometer based tilt sensors is that it is often difficult to determine whether the device is functioning properly. Many accelerometer based tilt sensors have built in self test modes that can verify proper functioning of the accelerometers. The weakness with these self test modes is that the accelerometer cannot react to inclination at the same time that it is in the test mode.
Another disadvantage of conventional tilt sensors is that, during installation, it often is difficult to precisely align the coordinate system of the accelerometers with the coordinate system of the desired measurements. Often such precision requires complicated manufacturing processes. Manufacturers often maintain precise control of the direction of the axes of the accelerometers with respect to the final assembled product. However, it is difficult to maintain the same level of precision between the accelerometer and the mounting points of the final product. Misalignment of the accelerometer's measuring axis reduces its sensitivity in the desired direction and increases cross-axis sensitivity, which is the sensitivity to acceleration in a direction orthogonal to the desired measurement axis.
Still another disadvantage of conventional tilt sensors is that it is difficult if not impossible to change the coordinate system of the final assembled product without changing the physical design so that it can be used in various applications with differing coordinate systems. The final product that measures tilt may be useful in many different products, each with its own coordinate system. Additionally, during the design phase of a product, the required mounting location and orientation of the tilt sensor may need to be changed. Because of these possibilities, it often is necessary to change coordinate systems without altering the tilt sensor.
It is therefore a primary object of the present invention to provide an accelerometer based tilt sensor that allows for error detection during normal operation.
Another primary object of the present invention is to provide a tilt sensor that can be easily aligned with and mounted on a device without the need for complicated manufacturing processes or adjustment of the tilt sensor components.
These and other objects will be apparent to those skilled in the art.